Book/Dissertation / PhD Thesis

FZJ-2021-02795

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Resolving interface effects in voltage controlled magnetic heterostructures using advanced neutron scattering and electron microscopy methods

Bhatnagar, T. (Corresponding author)FZJ*

2021
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-604-5

Please use a persistent id in citations: http://hdl.handle.net/2128/29254

Abstract: Voltage control of magnetism (VCM) shows a strong potential to impact the fieldof magnetic data storage and spintronic devices with low power consumption. Withthis as an aim, La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)O3 - PbTiO3 (LSMO/PMN-PT (001))heterostructure is deposited using oxide molecular beam epitaxy. LSMO is ferromagneticat room temperature. Grown on a piezoelectric /ferroelectric substratePMN-PT(001), it forms an artificial multiferroic heterostructure. This system wasstructurally characterized using different techniques revealing growth of epitaxialLSMO layers. The main part of this thesis focuses on the investigation of magnetoelectriccoupling in LSMO/PMN-PT(001). The measurements show change inthe nature of ME coupling, by varying different parameters like temperature anddirection of magnetization. In all experiments the voltage is applied along [001] direction.The magnetoelectric coupling in LSMO/PMN-PT(001) arises due to strainand charge coupling. Since the substrate PMN-PT is piezoelectric and ferroelectric,both strain effect and switching of ferroelectric polarizations contribute to the MEcoupling. Impact of both mechanism is visible in the measurements. Strain couplingis dominant along hard axis [100] of LSMO whereas charge coupling shows dominancealong easy axis [110] of LSMO. Using polarized neutron reflectometry (PNR),the magnetic depth profile as a function of applied voltage reveals the presence ofan interlayer with reduced nuclear scattering length density and magnetic scatteringlength density. Examining this interlayer with scanning transmission electronmicroscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) shows Ladeficiencyand excess of Mn near the interface with the dark regions to be particleswith a triangular cross-section. The stoichiometry of these particles is confirmedwith field cooled-cooling (FCC) curve which shows a jump in magnetization near theCurie temperature TC = 43K of Mn3O4. The formation of these particles is favoredwhen the LSMO films are strongly strained which leads to defects near the interface.STEM images shows the presence of defects near the interface. Real-space magneticfield mapping as a function of temperature is performed using off-axis electron holographyon LSMO/PMN-PT(001) which demonstrates uniform magnetic field in theLSMO films. The magnetic phase gradient reduces with increasing temperature depictingreduction in the magnetic field in LSMO layer with temperature. Based onsimilar approach, a second heterostructure, La0.7Sr0.3MnO3/ BaTiO3/ Nb:SrTiO3(LSMO/BTO/Nb:STO (001)) is deposited using high oxygen pressure sputteringsystem and oxide molecular beam epitaxy. Here, LSMO is a ferromagnetic component,BTO layer is ferroelectric and Nb:STO is used a conductive substrate. Thegrowth of this structure is a two-step process. The BTO layer is grown in thehigh oxygen pressure sputtering system using growth parameters optimized duringa growth study.

Note: Dissertation, RWTH Aachen University, 2021

---

Contributing Institute(s):

1. Streumethoden (JCNS-2)
2. Streumethoden (PGI-4)
3. JARA-FIT (JARA-FIT)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. 6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ) (POF4-6G4) (POF4-6G4)

Experiment(s):

1. MARIA: Magnetic reflectometer with high incident angle (NL5N)
2. TREFF: Neutronenreflektometer (NL5S)

Appears in the scientific report 2021

---

Database coverage:
;

---